This invention relates to apparatus for continuous or semicontinuous casting of molten metal into an ingot form.
In casting at least some metals, such as aluminum and alloys thereof, for example, the molten metal is poured into a mold having a bottom wall which is vertically movable. Typically, the sidewalls of the mold are short and situated at the top of a pit. When molten metal is flowed into the mold, it rapidly solidifies from the effect of a coolant, usually water, which is continuously sprayed on the mold exterior. The bottom wall or starting block is then lowered at a rate commensurate with the introduction of molten metal into the mold while a lubricant is continuously supplied to the interior sidewall surfaces of the mold to enhance lowering the ingot into the pit. Thus, a long ingot of metal is continuously produced. The supply of oil to lubricate between the interior of the mold and the solidified ingot surface is critical. In a method of providing oil, a continuous groove is cut in the top wall of the mold around the mold opening to function as a reservoir for oil. A plurality of slots are cut in the mold from the oil groove to the mold interior, and oil from the groove flows through the slots and down the interior mold surface. A cover plate or oil ring is fastened to the top surface of the mold over the oil reservoir groove in order to retain the oil therein. The inside dimensions of the oil ring are critical to insure that its assembly with the mold is suitable to enable lubrication of the mold and not interfere with the casting of the ingot.
The high temperatures incurred in molding cause the oil ring to expand but, heretofore, because of the manner of seating and attaching the oil ring to the mold, the periphery of the ring has been restrained against movement. Upon cooling to room temperature, the ring shrinks, and under some circumstances, it shrinks to an extent that it has lesser inside and outside dimensions than it had prior to being heated. If the mold is circular, for example, both the inside diameter and outside diameter decrease and the ring no longer fits properly with respect to the mold opening. In casting most aluminum alloys, water is used as a coolant and shrinkage of the oil ring has not been a major problem. In recent years, however, there has been an increasing interest in aluminum alloys having lithium as an alloying element, and ethylene glycol, rather than water, is often used as a coolant for safety reasons. For reasons that are not fully understood, the incidence of ring shrinkage has sharply increased when using ethylene glycol as a coolant. It is theorized that ethylene glycol is not as efficient as water for cooling, and the ring and other parts of the mold apparatus are thus used at a higher temperature level than when used with water. It is believed that this higher operating temperature adversely affects the shrinkage and expansion uniformity among the different parts of the casting mold package. For whatever reason, ring replacement is a problem when using ethylene glycol as a coolant in casting metal. It would be desirable to be able to reuse the ring by machining the ring interior an amount sufficient to increase the I.D. to its original value. Heretofore, however, there has been no practical way to reposition a machined ring with sufficient coaxial accuracy with respect to the mold to make it possible to salvage shrunken rings.
In addition to the problem created by shrinkage of the oil ring, molds can sometimes become deformed upon overheating. To use the mold, it has been necessary to either machine the mold to enable a concentric fit with an oil ring or hand fit the oil ring to the deformed mold. In either case, the salvage effort is time consuming and relatively costly.